The present invention relates to an apparatus for gravity-feed casting with a large number of ingot molds of metal billets of multiple diameters comprising at least two parallel rows of ingot molds.
Those skilled in the art are well aware of the process for continuous casting of metals in which molten metal is introduced into an externally cooled ingot mold provided with a movable bottom. While it is in the ingot mold, the metal sets and is discharged downwardly by means of the movable bottom while the ingot mold is supplied with fresh molten metal in its upper part so as to maintain an approximately constant level of molten metal in the mold.
To remedy certain operating difficulties many improvements have been made in that procedure such as those taught in French patent No. 1 364 776 and which comprise placing a reserve of liquid metal above the ingot mold in order to ensure that the dress or oxides which float on the free surface of the metal are not entrained into the resulting product where they would give rise to serious flaws. That gravity-feed reserve of metal which is also referred to as the feeder head reserve or "hot-top," also has the advantage of forming billets with a good surface condition. The use of a feeder head reserve or "hot-top" has been the subject of particular development in multiple-pouring apparatus since, with a single control in respect of level, it makes it possible to provide simultaneously for pouring metal into several tens of ingot molds at a time.
Generally, the feeder head overhangs the inside wall of the ingot mold, and means for continuously injecting gas or lubricant are disposed at the interface thereof to facilitate the casting operation and to improve the quality of the products produced. The following references are concerned with particular aspects of this invention.
In U.S. Pat. No. 3,381,741, the feed reservoir and the ingot mold are connected by way of a relatively thin, heat-conducting insert and means for introducing lubricant within the mold are disposed between the insert and the mold.
In U.S. Pat. No. 4,157,728, a gas is introduced below the overhang so as to apply a pressure to the periphery of the metal and a lubricating surface is provided within the mold by the introduction of a lubricant just below the means for introducing gas.
In U.S. Pat. No. 4,598,763, a flow of gas under pressure is supplied at a point disposed outside the cavity of a mold, the gas is discharged into the cavity at a point disposed at the periphery thereof and means such as a graphite ring are interposed between the supply point and the point of discharge on the outside of the cavity, to convert the flow of gas into a ring of fluid extending around the metal mass at the periphery of the cavity. In addition, lubricating oil is passed into the casting ladle, preferably passing through the overhang portion which is at the top of the ladle.
As applicants were concerned with the problem of casting metals using the gravity-feed or hot-top process and in particular casting billets of aluminum or aluminum alloy, it was noted on studying these references that the teaching thereof involved either using a continuous lubricating means and/or, when using gas under pressure, injection of the gas at the actual level of the ingot mold, by means of sophisticated regulating systems intended to prevent the pressure from rising beyond a limit which would give rise to movements within the liquid metal.
Being aware of the constraints imposed by these processes, applicants previously developed a simpler process and apparatus in which there is no need for continuous lubrication and the gas injection system is easier to regulate. These improvements were disclosed in EP No. 213 049 which was directed to the application of an inert gas pressure to the lower part of the periphery of the feeder head throughout the casting operation and the use of a feeder head formed by two parts which are connected together by way of a joint, with the lower part of the feeder head surrounded over its entire periphery by an annular chamber connected to a source of inert gas under pressure. These improvements contributed to a substantial improvement in the operation of casting installations and also the quality of the resulting products. However, there were still other problems which arose with the prior art apparatus which had to be overcome, in particular:
(1) Limiting the risks of explosion which are inherent in such installations. As in most casting apparatus, the metal which is undergoing solidification sticks to the wall of the mold and, by virtue of the fact that the metal is pulled downwardly under its own weight, can give rise to a movement of the mold which comes away from the feeder head. Thereby a space is created through which the cooling water can come into contact with the liquid metal and cause an explosive reaction; that danger was the subject of a communication from the Aluminum Association;
(2) In the case of installations having a plurality of flow passages, reducing the periods of time required for changing ingot molds, which are generally long and harmful to the level of productivity; and
(3) Providing the possibility of casting different formats while having to change only the ingot molds and the movable bottoms.